Process and apparatus for making porcelain inlays.



E. R. SCHROEDEII & c. M. MILLER.

PROCESS AND APPARATUS FOR MAKING PORCELAIN. INLAYS.

' APPLICATION FILED IAN. 25. I9I6.

. 1,211,244, I Patented Jan. 2, 1 917.

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' 5 scH a'snER mm x 7 Q BY A TTORNE vs.

YNE NORRIS PITIIIS Cd. PNIITO MIND" WASNINII'IJN. D. C I

PROCESS AND APPARATUS FOR MAKING PORCELAIN INLAYS.

Specification of Letters Patent.

Patented Jan. 2, 1917.

Application fi1ed January 25, 1916. Serial N 0. 74,127.

To all whom it may concern Be it known that we, Ennsr R. Scrrnonnnn and CHARLES M. MILLER, citizens of the United States of America, and residents of Alameda, county of Alameda, State of California, have invented a new and useful Process and Apparatus for Making Porcelain Inlays, of which the following is a specification.

Our invention relates to a new inethodof producing porcelain inlays in the practice of dental surgery.

An object of our invention is to provide improved means with which accurate inlays may be more easily obtained.

Another object of our invention is to provide an improved process for making inlays.

A further object of our invention is to provide a process for making porcelain inlays, by the practice of which the cavity in the tooth structure is accurately fitted by the inlay and perfect marginal contact between tooth and inlay is secured.

The invention possesses other features of advantage which, with the foregoing, will be set forth in the following description of the preferred form of our invention which is illustrated in the drawings accompanying and forming part of the specification. It is to be understood that we do not limit ourselves to the showing made by the said drawings and description, as we may adopt variations of the preferred form within the scope of our invention as set forth in the claims.

Referring to the drawingsz'Figure 1 is a view of a tooth showing a wax impression in the cavity which is to receive the inlay. Fig. 2 is a sectional view ofthe metal positive of the cavity cast from the wax pattern. Fig. 3 is a sectional view of the positive coated on the rear surface with wax. Fig. d is a sectional view through the mold, showing the wax coated positive invested therein. Fig. 5 is a. similar view after the wax has been elimin'atechshowing the mold ready to pour to form the negative of the tooth cavity. Fig. 6 is a sectional view of the negative or matrix casting. Fig. 7 is a sectional View 'of the negative filled with porcelain mixture, Fig. 8 is a sectional view through the porcelain inlay.

In broad outline our invention consists in providing a relatively heavy and rigid cast 3 .body or block having a cavity which is an exact duplicate of the cavity in the tooth so that the inlay which is prepared in this ma trix block or negative, may be transposed to the tooth cavity and will accurately fit therein and make perfect marginal contact therewith; and our invention further consists in the process by which said negative is formed and the process by which the inlay is prepared therein. 7

In practising our process, the cavity in the tooth is first properly excavated and prepared to the precise form intowhich it is desired to set the inlay. The cavity is then filled with wax 2, Fig. 1, the surface and margins of the wax filling being worked down and formed in exact similitude to the desired form of the inlay. By means of a pin 3 embedded therein the wax positive impression of the tooth cavity is withdrawn and a metallic positive 3, preferably of silver Fig. 2, is cast using the wax impression as a pattern so that the silver positive is an exact duplicate of the wax positive. The details of this process need not be given here since they are well known. It is seen that the silver positive which marks the completion of the first stage of our process, in itself constitutes an accurate silver inlay for the tooth cavity and the explanation will now be directed toward the process of producing in porcelain an exact duplicate of the silver positive.

In the process of casting the silver positive, a sprue 4 is'formed thereon which is on the outside of the positive if it is set in the tooth cavity. For convenience, this surface will be referred to hereafter as the outer surface, andthe surface which corresponds to the shape of the cavity will be called the rear surface.

A short portion of the sprue 4 is preferably left on the outer surface of the silver positive as shown in Fig. 3 and the rear surface is given a comparatively heavy coating of wax 5 in which a pin 6 and Wires 7 are embedded. Careful attention must be given to the edges of the wax where it contacts with the silver, for accuracy at the margins of the final product depends on the accuracy of contact between wax and silver about these edges. The wax coating is left' quite thick at the edges adjoining the outer surface and these edges are trimmed 01? at an angle determined by the adjacent portions 0f the outer surface of the positive so that the edges of the coating present a continuation of the outer surface of the positive of appreciable width. The pin 6 constitutes a sprue to form the ingate to the mold in following steps of the process and the wires 7 are to form ventsin the mold.

The silver positive with the wax coating and attached wires and pin'is now invested in a mold 8 of any suitable investment compound as shown in Fig. l and a cup 9 is hollowed out around the sprue to serve as a pouring gate. The sprue and vent wires are next withdrawn and the mold subjected to heat for the purpose of driving out the wax coating 5, in the manner which is Well understood bv persons familiar with the art to which this invention pertains. At this stage of our process. the mold 9 with the invested silver positive 3 therein, is as shown in Fig. 5. The purpose of having a short portion of the sprue 4: on the outer surface of the silver positive is now clear, since with the removal of the wax, it serves to retain the positive in proper position in the mold.

The mold as shown in Fig. 5 is now poured and for this casting we prefer to use gold or preferably by the action of a solvent which an alloy of gold and platinum for reasons which presently will be made clear. The details of securing this casting need not be explained at length as the methods by which this may be done are well known. The melted gold or alloy is preferably drawn into the mold either by vacuumizing the mold from below or by pressure or concussion above the mold, the essential thing being that the gold or alloy shall completely fill the space left by the evacuation of the wax so that the gold negative casting formed over the rear surface of the silver positive will5be an exact duplicate of the wax coatmg After cooling the mold is broken open and the silver positive is separated from the gold negative clinging to its rear surface,

will attack the silver but in which the gold is inert. For this we prefer to use nitric acid. The nitric acid dissolves the silver from the gold negative leaving the latter, as shown in Fig. 6, a matrix block or negative 12 in which the cavity 13 is an exact duplicate of the cavity in the tooth from which the first wax impression was made. With the securing of this matrix block the second stage of our process is completed. It will 'be understood that since the matrix block is a duplicate of the wax coating 5, it is only necessary to make the wax coating of the required thickness to insure that the matrix block will be amply strong and resistant to deformation in ordinary handling and use. This is of the utmost importance for deformation of the matrix however slight is destructive of accuracy in the inlay to that extent. With the matrix block of our invention, deformation of the inlay is wholly tooth curve, the edges 14: of the matrix block serving as guide and giving the proper di rection to the curve. Fig. 7 shows the matrix block with the completed porcelain inlay therein. After the formation of the porcelain inlay in the matrix block it is necessary to separate it from the block and this is preferably done by subjecting the block and inclosed porcelain to a solvent which will attack the gold or alloy, but in no way injure the porcelain. For this we prefer to use aqua regia and at the completion of this step of our process, the porcelain inlay as shown in Fig. 8 is secured. This is a duplicate, and on its rear surface which forms the margins, a minutely exact duplicate of the wax impression of the tooth cavity first taken; and on being cemented into the cavity will be found to give perfect marginal contacts. In

the above explanation the metals used in performing our invention are stated to be silver and gold, but our invention is not to be limited to the use of those metals, as other materials may be used. In case a porcelain is used which requires a heat in excess of the fusing point of gold, the negative or matrix block may be made of a gold or platinum alloy or other alloy possessed of the requisite resistance.

We claim 1. A form for baking and shaping a porcelain inlay for a given tooth cavity comprising a rigid cast matrix block having a recess therein the exact duplicate of the tooth cavity.

2. A form for baking and shaping a porcelain inlay for a given tooth cavity comprising a rigid cast matrix block formed of a material active in a reagent in which the inlay is inert and having a recess therein the exact duplicate of the tooth cavity.

3. The process of forming a porcelain inlay for a tooth cavity which consists in making a positive of said cavity, casting a rigid negative from said positive and forming said inlay in said negative.

4. The process of forming an inlay for a tooth cavity which consists in making a silver positive of said cavity, forming a rigid gold negative from. said positive, baking a porcelain mixture in said negative to form said inlay and dissolving said negative away from said inlay.

'5. The process of forming an inlay for a tooth cavity which consists in making a positive of said cavity, casting a negative upon said positive, removing the positive from the negative, treating a porcelain mixture in said negative to form said inlay and removing said negative from said inlay.

6. The process of forming an inlay for a tooth cavity which consists in making a silver positive of said cavity, casting a gold negative upon said positive, separating the positive from the negative by treating them with a solvent for the silver, heating a porcelain mixture in said negative to form saidinlay and separating the negative from the inlay by treating them with a gold solvent. 7. The process of forming an inlay for a tooth cavity which consists in making a wax positive of said cavity, casting a metallic positive therefrom, coating the rear surface of the metallic positive with wax, investing the coated positive in a mold, heating the mold to remove the wax, filling the cavity thus formed with a diiferent metal, remov- ERNST R. SCHROEDER. CHARLES MILLER.

In presence of EDWARD L. ,BRASWELL, H. URIMK.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

. Washington, D. 0. 

